1. Field of the Invention
The invention relates to a damping valve of the type having a one piece damping valve body with axial through passages for each direction of flow, a valve disk which at least partially covers outlet openings of through passages on at least one of said sides, and radial inflow openings for through passages.
2. Description of the Related Art
In the case of a damping valve in a piston-cylinder unit, especially a vibration damper, the aim is to make the through-passages or at least the cross sections at the outlet openings as large as possible. The installation space available for the through-passages in the damping-valve body of the damping valve is very limited. This has led to complex solutions that can often only be implemented by sintering if multi-component damping-valve bodies are used.
U.S. Pat. No. 5,259,294 discloses a sintered piston having two interengaging halves that together define the through-passages. With damping-valve bodies of this kind, there is, on the one hand, a need for complex sintering dies and, on the other hand, there is always the possibility that the damping-valve body will leak between the contact faces of the two halves of the piston. The complex form of the sintering dies is due to the fact that the through-passages have oblique sections.
An alternative to the oblique through-passages is known from DE 43 43 614 A1. The axially extending through-passages have a radial inflow opening. A significant disadvantage of this damping valve is that the inflow openings have to be machined into the damping-valve body. In this context, attention is also drawn to DE 196 21 639 A1.
Another possibility for creating large through-passages in a damping valve is known from DE 27 51 046 A1. The damping valve comprises two piston halves with through-passages for two directions of flow. Arranged on a radially outer pitch circle are axially extending inflow passages, the ends of which are connected to a common nonreturn valve. The nonreturn valve opens a transverse passage that leads to the through-passages with the outlet openings.
DE 40 33 186 A1 describes a restriction device with a bypass circuit dependent on the direction of motion that has axially extending through-passages in conjunction with radial inflow openings. Among the disadvantages of this restriction device is that measures have to be provided to prevent the valve disks sticking on the piston surface, e.g. by roughening the piston surface in the region of the valve disks. The through-passages or at least the outlet openings are furthermore kept relatively small, as a result of which the damping forces of the restriction device are relatively large.
It is the object of the present invention to obtain a damping valve that has a one-piece damping-valve body that requires little mechanical finish machining, if any, and has all possible fittings as regards its valve disks.
According to the invention, the outlet openings of the through-passages for a first direction of flow on one side of the damping-valve body have a trapezoidal cross section, and the outlet openings of the through-passages for a second direction of flow on the other side of the damping-valve body open into a common encircling annular channel. The through-passages with outlet openings with the trapezoidal cross section are arranged on a larger pitch circle than the through-passages that open into the annular passage.
The advantage of the new damping valve lies, on the one hand, in its simple damping-valve body and, on the other hand, in the large areas subjected to pressure on the valve disks. On the one hand, the sum of the trapezoidal cross sections should be regarded as one area subjected to pressure. The annular channel forms the area subjected to pressure for the valve disk for the other direction of flow. The larger pitch circle for the outlet openings of trapezoidal cross section represents a larger lever arm for the pressure acting on the valve disk. The annular passage acting in its entirety as an area subjected to pressure can therefore be made radially further inward and nevertheless produce the desired low damping force.
In order to minimize the area of contact for the valve disk for the first direction of flow and hence prevent sticking of the valve disk, the radial inflow openings are connected by an encircling channel at their radially inner ends.
In a further advantageous refinement, the outlet openings of trapezoidal cross section are framed by an encircling ridge, one portion of the encircling ridge bounding the encircling channel. The ridge forms support surfaces for the valve disk for the first direction of flow.
To achieve as large as possible a cross section for the damping medium flowing into the damping valve, the radial inflow openings are arranged between the outlet openings of trapezoidal cross section, an adjoining portion of the through-passage being embodied as a funnel. The funnel is a shape that is easy to form and allows advantageous deflection of the damping medium from the radial inflow opening into the axial through-passage.
According to another advantageous embodiment, the funnel of the through-passage is framed over an arc segment by the encircling ridge of the outlet opening of trapezoidal cross section. The aim of this measure is to achieve as large as possible a funnel opening. For this purpose, it is advisable for the funnel to extend right up to the trapezoidal outlet openings arranged in the circumferential direction and to cancel out the pure trapezoidal shape at said arc segment.